Effect of Solder Mask Surface Chemistry and Morphology on the Water Layer Formation Under Humid Conditions

This paper investigates the water film buildup on solder masked printed circuit board assembly (PCBA) laminates under humid conditions. The effects of solder mask surface chemistry, morphology, and roughness were investigated using different commercial laminates coated with solder mask. Chemical composition of the materials was analyzed using Fourier transform infrared spectroscopy. Microstructure and surface morphology were investigated using scanning electron microscopy, whereas the wettability was assessed using static contact angle technique, and correlated with the morphological observations. Solder mask surface waviness was characterized and quantified using a mechanical stylus profilometer. The formation of water film on a PCBA surface was monitored in situ by optical microscopy and electrochemical impedance spectroscopy and correlated with the observations of surface features. The results show that the solder mask surface chemistry and morphology significantly influence the water film formation, which is important for corrosion reliability of electronics exposed to humid conditions.